The invention relates to new ferroelectric or high dielectric, chiral smectic liquid crystal compounds to be used for a display element or an electrooptical element, with utilizing the particular property that the molecular orientation thereof can be controlled in an electric field.
The liquid crystal display element has been widely used for various purposes as well known owing to desired properties thereof such as low electric tension workability, low electric energy consumption, displayability in a thin form, and light recepting type causing less eyestrain.
A liquid crystal display device of twisted nematic (TN) type is, however, not satisfactory in that the speed of response is too slow in comparison with display devices of light emitting type such as a cathode ray tube (CRT) so that use thereof is rather restricted for that purpose.
As an improvement of said property of such nematic liquid crystals, R. B. Meyer et al succeeded in the year of 1975 to synthesize decylooxybenzylidene-amino-2-methylbutyl cinamates (DOBAMBC) as ferroelectric liquid crystals. In the year of 1980, Clark and Lagawall found and confirmed a high speed switching property in the order of a microsecond of the DOBAMBC thin film cell.
These ferroelectric chiral smectic liquid crystals have a high speed of response about 100 times that of the nematic ones conventional since then as well as good bistability so as to be applied to various display devices for moving pictures such as TV, high speed photoshutters and so on.
It is necessary as the ferroelectric liquid crystal, to have spontaneous polarization which is inversible by an electric field, chiral molecular structure, particular smectic layer and a dipole moment component in the vertical direction to the line of apsides of the liquid crystal molecule.
Followings have been known in relation thereto regarding how to make molecular designs in order to obtain liquid crystals having not only high dielectricity but also large spontaneous polarization;
(1) Since the rotation of liquid crystal molecule about the line of apsides may reduce efficient orientation degree of dipole moment so that spontaneous polarization is resultingly made smaller, it is effective to supress the molecule free rotation. For that purpose, it is possible to introduce a bulky atomic or molecular group in the vicinity of an asymmetric carbon atom.
(2) It may be a direct method for obtaining large spontaneous polarization to cause large dipole moment in the vicinity of the asymmetric carbon atom, for which an atomic or molecular group of fluorine such as CF.sub.3 is directly introduced at the asymmetric carbon atom.